Fiber optic energy sensor and optical demodulation system and methods of making same

Abstract

A fiber optic energy sensor and optical demodulation system is disclosed wherein the signal energy to be sensed or detected causes an etched single mode fiber to be stretched or compressed which causes the optical path length for electromagnetic radiation traveling in the core of the optic fiber to change. The change in optic path length modulates the electromagnetic radiation traveling in the fiber. There is also disclosed novel methods of manufacturing the novel type of fiber optic energy sensor and optical demodulation system.

We claim: 
     
       1. The method of spectrally amplifying the spectral shift of the transmission peaks of a Fabry-Perot interferometer comprising: projecting or guiding wavelength scanned electro-magnetic radiation into the said Fabry-Perot interferometer;   projecting the spectrally shifted transmitted output peaks of the Fabry-Perot interferometer into an analyzer Fabry-Perot interferometer; and   constructing the cavity length of said Fabry-Perot interferometer and said analyzer Fabry-Perot interferometer in accordance with the following equations: ##EQU16##   Δλ.sub.SA ≈UΔλ.sub.SR    EQ XI ##EQU17## for S.sub.A =(f)(S.sub.R)±1     and     S A  and S R  >2 and f is a positive integer.   
     
     
       2. The method defined in claim 1 further including a method for eliminating ambiguous outputs comprising: dividing the transmitted electro-magnetic radiation of the Fabry-Perot interferometer into at least two separate beams;   projecting each beam into a separate analyzer Fabry-Perot interferometer; and   arranging the spectral separation of the transmission peaks of each analyzer Fabry-Perot interferometer relative to that of the Fabry-Perot interferometer so as to cause spectral amplification of the resulting output of each analyzer Fabry-Perot interferometer so that the amplification caused by each analyzer Fabry-Perot interferometer is different from that caused by all others.   
     
     
       3. The method defined in claim 1 for producing an electrical output comprising: projecting the output electromagnetic radiation of the analyzer Fabry-Perot interferometer onto a photodetector the output of which is an electric signal and the amplitude of which is a function of the amplitude of the radiation incident thereon;   conducting the electrical output of the photodetector to an electrical lead of a separate time demodulator; and   conducting an electrical reference signal to the electrical lead of the selected demodulator.   
     
     
       4. The method defined in claim 3 comprising: projecting a portion of the wavelength scanned electro-magnetic radiation into a reference Fabry-Perot interferometer; and   projecting the transmitted output radiation of the reference Fabry-Perot interferometer onto a photodetector the output of which is an electrical signal and the amplitude of which is a function of the incident amplitude and which is used as the electrical reference signal.   
     
     
       5. The method defined in claim 1 comprising: using optical fiber and a pair of length limited Bragg reflectors to form a Fabry-Perot type interferometer   using optical fiber and a pair of length limited Bragg reflectors to form a Fabry-Perot type interferometer having the optical fiber as its cavity so that the Fabry-Perot type interferometer has a region of transmission peaks which is spectrally within the wavelength scanned range of the electromagnetic radiation; and   replacing the Fabry-Perot interferometer with the Fabry-Perot type interferometer.   
     
     
       6. The method defined in claim 5 comprising: using at least two pairs of length limited Bragg reflectors each of which forms a separate Fabry-Perot type interferometer and each having a different longitudinal location on the same optical fiber; and   arranging the reflection wavelength bands of the reflector pairs to be different from each other and so that at least one reflection band of each reflector pair is spectrally within the wavelength scanned range of the electromagnetic radiation.   
     
     
       7. The invention defined in claim 1 further comprising a wavelength scanning laser to produce the said wavelength scanned electromagnetic radiation. 
     
     
       8. The invention defined in claim 9 further comprising a wavelength scanning laser to produce the wavelength scanned electro-magnetic radiation. 
     
     
       9. A means for amplifying the spectral shift of the transmission peaks of Fabry-Perot interferometer comprising: a beam of wavelength scanned electromagnetic radiation directed into the Fabry-Perot interferometer having spectrally shifted transmission peaks;   an analyzer Fabry-Perot interferometer, placed so the resulting transmitted output of the said Fabry-Perot interferometer is directed to said analyzer Fabry-Perot interferometer constructed to have a cavity length related to the cavity length of said Fabry-Perot interferometer in accordance with the following equations: ##EQU18##   Δλ.sub.SA ≈UΔλ.sub.SR    EQ XI ##EQU19## for S.sub.A =(f)(S.sub.R)±1     and     S A  and S R  >2 and f is a positive integer.   
     
     
       10. The invention defined in claim 9 further including means for decreasing ambiguity comprising: at least one beamsplitter oriented to divide the transmitted electro-magnetic radiation of the Fabry-Perot interferometer into at least two partial beams;   at least one additional analyzer Fabry-Perot interferometer positioned so that a separate partial beam is projected into it and each of which is arranged to have a transmission peak spectral separation relative to the Fabry-Perot interferometer to cause a spectral amplification which is different from that caused by the other analyzer Fabry-Perot interferometers.   
     
     
       11. The invention defined in claim 9 further including means for producing an electrical output comprising: a photodetector oriented so that the output electromagnetic radiation of the analyzer Fabry-Perot interferometer is incident on it; and   a time demodulator into which is conducted an electrical reference signal and the electrical output of the said photodetector.   
     
     
       12. The invention defined in claim 11 further comprising: a reference Fabry-Perot interferometer; and   another photodetector oriented so that its output is an electrical signal, the amplitude of which is a known function of the amplitude of the output of the reference Fabry-Perot interferometer which is incident on it.   
     
     
       13. The invention defined in claim 9 further comprising: an optical fiber;   a pair of optical fiber length limited Bragg reflectors constructed within the optical fiber to form a Fabry-Perot type interferometer so that the Fabry-Perot type interferometer has a region of transmission peaks which is spectrally within the wavelength scanned range of the electromagnetic radiation.   
     
     
       14. The invention defined in claim 13 further comprising: at least one additional pair of length limited Bragg reflectors, each pair of which forms a Fabry-Perot type interferometer each of which has a different longitudinal location along the optical fiber and has a region of transmission peaks which is spectrally within the wavelength scanned range of the electromagnetic radiation but outside of like regions of each other Fabry-Perot type interferometer located on the same fiber.